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Importance of secondary organic aerosol formation of iα/i-pinene, limonene, and im/i-cresol comparing day- And nighttime radical chemistry
2021, Mutzel, Anke, Zhang, Yanli, Böge, Olaf, Rodigast, Maria, Kolodziejczyk, Agata, Wang, Xinming, Herrmann, Hartmut
The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate span classCombining double low line"inline-formula"iα/i/span-pinene, limonene, and span classCombining double low line"inline-formula"im/i/span-cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NOspan classCombining double low line"inline-formula"3/span radicals) and daytime conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NOspan classCombining double low line"inline-formula"3/span under dry conditions significantly exceeds that of the OH-radical reaction, with SOA yields of 15-30 % and 10-21 %, respectively. Additionally, the nocturnal SOA yield was found to be very sensitive towards RH, yielding more SOA under dry conditions. In contrast, the SOA formation potential of span classCombining double low line"inline-formula"iα/i/span-pinene with NOspan classCombining double low line"inline-formula"3/span slightly exceeds that of the OH-radical reaction, independent from RH. On average, span classCombining double low line"inline-formula"iα/i/span-pinene yielded SOA with about 6-7 % from NOspan classCombining double low line"inline-formula"3/span radicals and 3-4 % from OH-radical reaction. Surprisingly, unexpectedly high SOA yields were found for span classCombining double low line"inline-formula"im/i/span-cresol oxidation with OH radicals (3-9 %), with the highest yield under elevated RH (9 %), which is most likely attributable to a higher fraction of 3-methyl-6-nitro-catechol (MNC). While span classCombining double low line"inline-formula"iα/i/span-pinene and span classCombining double low line"inline-formula"im/i/span-cresol SOA was found to be mainly composed of water-soluble compounds, 50-68 % of nocturnal SOA and 22-39 % of daytime limonene SOA are water-insoluble. The fraction of SOA-bound peroxides which originated from span classCombining double low line"inline-formula"iα/i/span-pinene varied between 2 and 80 % as a function of RH./p pFurthermore, SOA from span classCombining double low line"inline-formula"iα/i/span-pinene revealed pinonic acid as the most important particle-phase constituent under day- and nighttime conditions with a fraction of 1-4 %. Other compounds detected are norpinonic acid (0.05-1.1 % mass fraction), terpenylic acid (0.1-1.1 % mass fraction), pinic acid (0.1-1.8 % mass fraction), and 3-methyl-1,2,3-tricarboxylic acid (0.05-0.5 % mass fraction). All marker compounds showed higher fractions under dry conditions when formed during daytime and showed almost no RH effect when formed during night./p © 2021 Copernicus GmbH. All rights reserved.
The acidity of atmospheric particles and clouds
2020, Pye, Havala O.T., Nenes, Athanasios, Alexander, Becky, Ault, Andrew P., Barth, Mary C., Clegg, Simon L., Collett Jr, Jeffrey L., Fahey, Kathleen M., Hennigan, Christopher J., Herrmann, Hartmut, Kanakidou, Maria, Kelly, James T., Ku, I-Ting, McNeill, V. Faye, Riemer, Nicole, Schaefer, Thomas, Shi, Guoliang, Tilgner, Andreas, Walker, John T., Wang, Tao, Weber, Rodney, Xing, Jia, Zaveri, Rahul A., Zuend, Andreas
Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semivolatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine-particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicate acidity may be relatively constant due to the semivolatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale. © 2020 Author(s).
Impact of water uptake and mixing state on submicron particle deposition in the human respiratory tract (HRT) based on explicit hygroscopicity measurements at HRT-like conditions
2022, Man, Ruiqi, Wu, Zhijun, Zong, Taomou, Voliotis, Aristeidis, Qiu, Yanting, Größ, Johannes, van Pinxteren, Dominik, Zeng, Limin, Herrmann, Hartmut, Wiedensohler, Alfred, Hu, Min
Particle hygroscopicity plays a key role in determining the particle deposition in the human respiratory tract (HRT). In this study, the effects of hygroscopicity and mixing state on regional and total deposition doses on the basis of the particle number concentration for children, adults, and the elderly were quantified using the Multiple-Path Particle Dosimetry model, based on the size-resolved particle hygroscopicity measurements at HRT-like conditions (relative humidity = 98 %) performed in the North China Plain. The measured particle population with an external mixing state was dominated by hygroscopic particles (number fraction = (91.5 ± 5.7) %, mean ± standard deviation (SD); the same below). Particle hygroscopic growth in the HRT led to a reduction by around 24 % in the total doses of submicron particles for all age groups. Such a reduction was mainly caused by the growth of hygroscopic particles and was more pronounced in the pulmonary and tracheobronchial regions. Regardless of hygroscopicity, the elderly group of people had the highest total dose among three age groups, while children received the maximum total deposition rate. With 270 nm in diameter as the boundary, the total deposition doses of particles smaller than this diameter were overestimated, and those of larger particles were underestimated, assuming no particle hygroscopic growth in the HRT. From the perspective of the daily variation, the deposition rates of hygroscopic particles with an average of (2.88 ± 0.81) × 109 particles h-1 during the daytime were larger than those at night ((2.32 ± 0.24) × 109 particles h-1). On the contrary, hydrophobic particles interpreted as freshly emitted soot and primary organic aerosols exhibited higher deposition rates at nighttime ((3.39 ± 1.34) × 108 particles h-1) than those in the day ((2.58 ± 0.76) × 108 particles h-1). The traffic emissions during the rush hours enhanced the deposition rate of hydrophobic particles. This work provides a more explicit assessment of the impact of hygroscopicity and mixing state on the deposition pattern of submicron particles in the HRT. Copyright:
CAPRAM reduction towards an operational multiphase halogen and dimethyl sulfide chemistry treatment in the chemistry transport model COSMO-Muscat(5.04e)
2020, Hoffmann, Erik H., Schrödner, Roland, Tilgner, Andreas, Wolke, Ralf, Herrmann, Hartmut
A condensed multiphase halogen and dimethyl sulfide (DMS) chemistry mechanism for application in chemistry transport models is developed by reducing the CAPRAM DMS module 1.0 (CAPRAM-DM1.0) and the CAPRAM halogen module 3.0 (CAPRAM-HM3.0). The reduction is achieved by determining the main oxidation pathways from analysing the mass fluxes of complex multiphase chemistry simulations with the air parcel model SPACCIM (SPectral Aerosol Cloud Chemistry Interaction Model). These simulations are designed to cover both pristine and polluted marine boundary layer conditions. Overall, the reduced CAPRAM-DM1.0 contains 32 gas-phase reactions, 5 phase transfers, and 12 aqueous-phase reactions, of which two processes are described as equilibrium reactions. The reduced CAPRAM-HM3.0 contains 199 gas-phase reactions, 23 phase transfers, and 87 aqueous-phase reactions. For the aqueous-phase chemistry, 39 processes are described as chemical equilibrium reactions. A comparison of simulations using the complete CAPRAM-DM1.0 and CAPRAM-HM3.0 mechanisms against the reduced ones indicates that the relative deviations are below 5 % for important inorganic and organic air pollutants and key reactive species under pristine ocean and polluted conditions. The reduced mechanism has been implemented into the chemical transport model COSMO-MUSCAT and tested by performing 2D simulations under prescribed meteorological conditions that investigate the effect of stable (stratiform cloud) and more unstable meteorological conditions (convective clouds) on marine multiphase chemistry. The simulated maximum concentration of HCl is of the order of 109 molecules cm−3 and that of BrO is around 1×107 molecules cm−3, reproducing the range of ambient measurements. Afterwards, the oxidation pathways of DMS in a cloudy marine atmosphere have been investigated in detail. The simulations demonstrate that clouds have both a direct and an indirect photochemical effect on the multiphase processing of DMS and its oxidation products. The direct photochemical effect is related to in-cloud chemistry that leads to high dimethyl sulfoxide (DMSO) oxidation rates and a subsequently enhanced formation of methane sulfonic acid compared to aerosol chemistry. The indirect photochemical effect is characterized by cloud shading, which occurs particularly in the case of stratiform clouds. The lower photolysis rate affects the activation of Br atoms and consequently lowers the formation of BrO radicals. The corresponding DMS oxidation flux is lowered by up to 30 % under thick optical clouds. Moreover, high updraught velocities lead to a strong vertical mixing of DMS into the free troposphere predominately under cloudy conditions. The photolysis of hypohalous acids (HOX, X = Cl, Br, or I) is reduced as well, resulting in higher HOX-driven sulfite-to-sulfate oxidation in aerosol particles below stratiform clouds. Altogether, the present model simulations have demonstrated the ability of the reduced mechanism to be applied in studying marine aerosol–cloud processing effects in regional models such as COSMO-MUSCAT. The reduced mechanism can be used also by other regional models for more adequate interpretations of complex marine field measurement data.
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume VII-Criegee intermediates
2020, Cox, R. Anthony, Ammann, Markus, Crowley, John N., Herrmann, Hartmut, Jenkin, Michael E., Faye McNeill, V., Mellouki, Abdelwahid, Troe, Jürgen, Wallington, Timothy J.
This article, the seventh in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers an extension of the gas-phase and photochemical reactions related to Criegee intermediates previously published in Atmospheric Chemistry and Physics (ACP) in 2006 and implemented on the IUPAC website up to 2020. The article consists of an introduction, description of laboratory measurements, a discussion of rate coefficients for reactions of O3 with alkenes producing Criegee intermediates, rate coefficients of unimolecular and bimolecular reactions and photochemical data for reactions of Criegee intermediates, and an overview of the atmospheric chemistry of Criegee intermediates. Summary tables of the recommended kinetic and mechanistic parameters for the evaluated reactions are provided. Data sheets summarizing information upon which the recommendations are based are given in two files, provided as a Supplement to this article. © Author(s) 2020.
The evolution of cloud and aerosol microphysics at the summit of Mt. Tai, China
2020, Li, Jiarong, Zhu, Chao, Chen, Hui, Zhao, Defeng, Xue, Likun, Wang, Xinfeng, Li, Hongyong, Liu, Pengfei, Liu, Junfeng, Zhang, Chenglong, Mu, Yujing, Zhang, Wenjin, Zhang, Luming, Herrmann, Hartmut, Li, Kai, Liu, Min, Chen, Jianmin
The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and the behaviours of clouds and their influence on climate. In an attempt to better understand the microphysical properties of cloud droplets, the simultaneous variations in aerosol microphysics and their potential interactions during cloud life cycles in the North China Plain, an intensive observation took place from 17 June to 30 July 2018 at the summit of Mt. Tai. Cloud microphysical parameters were monitored simultaneously with number concentrations of cloud condensation nuclei (NCCN) at different supersaturations, PM2:5 mass concentrations, particle size distributions and meteorological parameters. Number concentrations of cloud droplets (NC), liquid water content (LWC) and effective radius of cloud droplets (reff) show large variations among 40 cloud events observed during the campaign. The low values of reff and LWC observed at Mt. Tai are comparable with urban fog. Clouds on clean days are more susceptible to the change in concentrations of particle number (NP), while clouds formed on polluted days might be more sensitive to meteorological parameters, such as updraft velocity and cloud base height. Through studying the size distributions of aerosol particles and cloud droplets, we find that particles larger than 150 nm play important roles in forming cloud droplets with the size of 5-10 μm. In general, LWC consistently varies with reff. As NC increases, reff changes from a trimodal distribution to a unimodal distribution and shifts to smaller size mode. By assuming a constant cloud thickness and ignoring any lifetime effects, increase in NC and decrease in reff would increase cloud albedo, which may induce a cooling effect on the local climate system. Our results contribute valuable information to enhance the understanding of cloud and aerosol properties, along with their potential interactions on the North China plain. © Author(s) 2020.